Unraveling the role of coordinated water in the capture of americium and toxic gases by an ultrastable uranyl phosphonate framework

Abstract

The design and fabrication of uranium phosphonate frameworks (UPFs) pave a potential avenue to reduce the environmental risk of depleted uranium, transuranium waste, and toxic gases while adding to its waste to utility virtues. However, it remains unknown how the pervasive coordinated water of UPFs influences their performances in radionuclide and toxic gas separation. Toward this end, we prepared a new category of porous UPFs, namely UPF-205 with abundant coordinated water and resulting hydrogen bonding nanotraps. The coordinated water is synergistic in quantitatively removing trivalent f-elements (i.e., Am3+, Eu3+) from wide-ranging pH solutions together with proximal phosphonate groups at a low metal concentration. Most importantly, an unprecedented coordinated water-mediated Eu3+-UO22+ transmetalation had been verified at a relatively high metal concentration. The high-density open uranyl sites and optimal pore size triggered by the dehydration of coordinated water also contribute to the enhanced adsorption of toxic SO2 and NH3. Our work shows great relevance for the rational design of ultrastable UPFs as both depleted uranium waste forms and efficient adsorbents for radiological/nuclear protection.